An ultrasonic diagnostic apparatus is for receiving, by an ultrasonic probe, reflected waves (echo) formed by ultrasonic waves transmitted from the same ultrasonic probe and reflected within a living body, and constructing a tomographic image of the inside of the living body based on the outputted echo signals from the probe. Generally, echo signals have a wide dynamic range (for example, 100˜120 dB). For example, while a signal from a superficial portion of a body surface exceeds 1V, a signal from a deep portion is only around several μV which is small, whereby the signal level received by the ultrasonic probe is extensive. The fact that the level of echo signals covers a wide range as mentioned above is a source of characteristics of the ultrasonic diagnostic apparatus that excels in rendering soft tissues. Consequently, in ultrasonic diagnostic apparatus, finding a way to render without diminishing a wide range of echo signal levels is a cornerstone in system designing.
Generally, while an echo received by an ultrasonic probe is converted into an electronic signal and amplified in a preamplifier, the scope of the upper and lower limit of the signal level possible to input to the preamplifier (hereinafter abbreviated as an input range) is specified. Therefore, for example, in the case that echo signals exceeding the input range such as the echo signals from superficial portion of the body surface like a fat layer are assumed to be inputted to the preamplifier, saturation of the preamplifier is avoided by suppressing the echo signals within the input range of the preamplifier using devices such as diode clipping circuit or diode attenuator.
On the other hand, while echo signals from a deep portion of a body tend to be attenuated and become negligible in the propagation process, the echo signals from a deep portion receive implementation for compensating the intensity by a device such as a TGC (Time Gain Control) amplifier provided with a characteristic of increasing amplification degree more on the echo signals from the deep portion than those from the shallow portion.
Patent Document 1: U.S. Pat. No. 6,246,158B1